Date: Fri, 21 Sep 2001 11:10:30 -0400 From: Joe Abley <jabley@automagic.org> To: JINMEI Tatuya / ??????????? <jinmei@isl.rdc.toshiba.co.jp> Cc: freebsd-net@FreeBSD.ORG Subject: Re: ipv6/gif/cisco syslog noise Message-ID: <20010921111029.H4205@buffoon.automagic.org> In-Reply-To: <y7vadzopq9h.wl@condor.jinmei.org> References: <20010919153739.K85635@buffoon.automagic.org> <20010920.050441.28824742.ume@mahoroba.org> <20010919164416.Q85635@buffoon.automagic.org> <y7vadzopq9h.wl@condor.jinmei.org>
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On Fri, Sep 21, 2001 at 11:33:46PM +0900, JINMEI Tatuya / ??????????? wrote: > >>>>> On Wed, 19 Sep 2001 16:44:18 -0400, > >>>>> Joe Abley <jabley@automagic.org> said: > > jabley> The tunnel is configured like this: > >> > jabley> buffoon# ifconfig gif0 > jabley> gif0: flags=8011<UP,POINTOPOINT,MULTICAST> mtu 1280 > jabley> inet6 fe80::2d0:b7ff:fe79:a0a7%gif0 --> :: prefixlen 64 scopeid 0x4 > jabley> inet6 2001:438:1fff:ffff:8::32 --> 2001:438:1fff:ffff:8::31 prefixlen 126 > >> > >> It should be /128. > > > Problem solved. Thanks :) > > Out of curiosity, why did you use /126 in the former configuration? > We're now discussing how the kernel should treat IPv6 global addresses > on a p2p link, and we are interested in actual users' intentions. I spend my waking hours arm-deep in cisco and Juniper routers, and those (and other) vendors frequently do not distinguish between ptp and (nb)ma networks in terms of addressing. In this case, on the cisco router which terminates the tunnel, defining the tunnel interface with a 126-bit netmask causes a /126 prefix to be distributed in the IGP, and this provides reachability information for both ends of the tunnel to other routers in the network. If the cisco interface had been numbered with a 128-bit netmask, a /128 prefix would have been distributed which would have provided reachability information for the cisco tunnel interface, but not the FreeBSD gif interface. Hence traffic sourced from the FreeBSD box using that gif interface address as a source address would not get replies routed correctly. My reason for using a 126-bit netmask on the FreeBSD router was mainly due to familiarity with the cisco/juniper way of doing things. I see that when I configure a gif interface with a 128-bit netmask and specify a destination, I get two host routes in the kernel (one for each end of the tunnel). This seems equally valid as far as propagation of the routes is concerned. The reason for allocating four addresses (a 126-bit prefix) to the point-to-point link stems from similar practice in IPv4, I think (it wasn't my decision; it's current policy in AS6461). Joe To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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